Differential rudder for airplanes



Dec. 1, 1942- c. L. JOHNSON DIFFERENTIAL RUDI DER FOR AIRPLANES Filed July 22; 1940 Flam [NVENTUQ Powwo 1, 1942 UNITED -sTArEs PATENT o DIFFERENTIAL RUDDER FOR AIRPLANES Clarence L. Johnson, Burbank, Calm, assignor to Lockheed Aircrait'corporation, Burbank, Calif.

Application July 2 2, 1940, Serial No. 346,787

2 Claims. (Cl. 244-83 This invention relates to an improved form of combined directional and lateral control for airplanes, comprising a diflerential or split rudder for producing various combinations or turning, rolling, and banking movements of the airplane.

In the control of airplanes it has been customary to; utilize hinged ailerons forming portions In the drawing:

Figure I is a side elevation of an airplane 'embodying the twin rudders 01 this invention.

Figure II'is a plan view thereof.

Figures 111 and IV' illustrate simultaneous and opposed movements respectively of the twin rudders,,which are adjustable to intermediate duced by opposing movements of the ailerons andrudder may cause a stall.

It is accordingly an object of this inyention to provide a pair of independent rudders disposed on opposite sides of a longitudinal axis of the airplane, whereby lat ral control of the airplane may buaried fr m apure roll-without a yawing tendency, through various combinations of banks and turns, to a pure'turning' movement;

eliminating, or greatly reducing, the need of wing positions between these extremes.

Figure. V is a, perspective diagrammatic showing of a control mechanism for operating the twin-rudders through the range between rolling and turning movements, I

As shown:

A complete airplane structure is shown in Figures I and II to illustrate the installation of the rudders of this invention, it being understood tliat details of the type and arrangement of the airplane per se have no bearing on the present invention, which is adaptable to various other types of aircraft. The airplane chosen tor illustrative purposes comprises a fuselage IO having monoplane wings II, a tricycle landing tip ailerons and thereby increasingthe available wing space for wing flaps or other high lift devices increasingly needed for satisfactory take- "off and landing characteristics, as designers strive for higher speeds. a

It is another object oi this invention to provide an improved airplane control means for operating'oppositely positioned rudders, the control v means'being variable through the range from simultaneous to opposing movements of the rud ders:

It is a further object of this invention to pro-. 1

vide an improved directional and .lateral'con- ..trol means for airplanes wherein oppositely disposed ruddersmay .be operated independently or together to produce various combinations of turns and rolls: or banks, the controls being such that ailerons, if used, may be simultaneously operated incorrect relationship with rolling move-' ments produced by the rudders.

Other and further important objects of indescribed.

provide trimming tabs gear l2, a tractor propeller I3, a horizontal stabilizer l4. and elevators l5.

Upper and lower vertical stabilizers rudders I! which are independently pivoted th'ereto, the rudders being preferably movable over a rearward extension i8 of the horizontal stabilizer it. It is not essential to this invention that the vertical stabilizers I 6 beused, as the rudders H can provide sumcient vertical surface for stabilizing'purposes; and the rudders need .not be hinged at their forward edges as shown, butmay be more or less balanced about a vertical pivot, thus functioning as adjustable fins. While the rudders I! are shown as of substantially the same .size, it will be evident that one may be appreciablylarger than the other if more fin area is desired above or below the fuselage. 'I'h'e rearward stabilizer extension 18 iswnot essential, the only requirement being to prevent interference between the elevators and rudders in their extreme angular positio I 9 on the rear edges of the rudders l1, either or both of which tabs are adjustable to compensate for engine torque re-. action.

the elevators I5.

5 The use of spaced diiferentially movable rudders permits the reduction in size or entire elimination of conventional ailerons near the outer together to assist in rolling endsof thetrailing edges of the wings II. It is also'possibleto operate the rudders and ailerons and yawing move- 111811158, or the rudders can-be used in opposition FFICE,

I6 carry It is customary to Similar'trimming tabs 20 are shown 'on to the ailerons to correct the yawing tendency introduced by the ailerons alone. If ailerons are area for take-off and landing, and being essen-.

tial to reduce the landing speed in high performance airplanes.

The spaced rudders may be operated differentially or in unison by a combined foot pedal and stick mechanism, as shown in Figure V, In this figure, separate foot pedals 23 have duplicate control cables 24 and 25 to operating bars 26 on the upper and lower rudders, the cables being led over stationary pulleys-21 to upper and lower,

pulleys 28 and 29 equally distant from a pivot point'30 of a control stick 3|. The stick 3| is also pivoted on a traverse axis.32 for a conventional control of the elevators l 5 which control has been omitted from the drawing to avoid confusion. It will be evident that the elevators l5 couldbe given a differential movement of the same type as disclosed herein for the rudders; and that ailerons, if used could also be controlled by the stick 3| in the usual manner.

In the operation of the spaced rudders it will be convenient to first trace the control for the upper rudder, bearing in mind that the cables 24 therefor are duplicated on each side. Assuming that the rudders are to be pivoted counterclockwise for a right turn, the lower pedal is pushed forward, the cable linkage pulling the I other pedal back to the same extent. As long as the control stick 3| is held in--neutral, both upper and lower rudders will be turned in the same direction and to the same extent. If the stick M is now tilted towards the left it will tend to slack off on the near side upper cable 25 and tighten up on the near side lower cable 24 thus It will be evident that the symmetrical rudder arrangement provides for a true rolling movement on the axis of the plane without introducing yawing components that require opposite rudder to maintain a true course.

Having thus described my invention and the present preferred embodiment thereof, I desire to emphasize the fact that many modifications may be resorted to in a manner limited onlyby a just interpretation of the following claims. A

I claim: I

1., In an airplane, a pair of substantially aligned control surfaces separately pivoted on opposite sides of the longitudinal axis of the airplane, control means for normally operating said control surfaces in unison to alter the direction of said airplane axis, comprising a pair of pedals each connected by cable systems to each of said control surfaces, and means for varying the response of each control surface to the pedal movements, comprising a pivoted control member having pulleys linked thereto on opposite sides of the pivot respectively and linked in the cable systems ex.-

tending to the control surfaces on the corresponding'sides of. the airplane axis whereby a movement of the control member about its pivot isadapted to shorten one side and correspondingly lengthen the other side of the cable systems connecting the pedals to one control-surface while correspondingly lengthening one side and shortening the other side of the cable systems for the opposite-control surface.

- 2. In an airplane, in combination, a fuselage, a pair of fixed vertically extending stabilizing surfaces positionedadjacent the rear end of said fuselage and having a longitudinal lever arm relative to the center of gravity of the airplane, said surfaces being arranged one above and the other, below the longitudinal axis of the fuselage, a pair of rudder surfaces separately pivoted to the rear edges of said stabilizing surfaces, means includtending to decrease the angle of the upper rudder and increase the angle of the lower rudder. At

the same time the far side cables are oppositely affected so that no actual slack is developed in the control cables by stick movement. It will be evident that the pedals and stick can be operated simultaneously or separately, the stick providing for pure rolling movements, the pedals for a flat turn, and combinations thereof providing a differential rudder movement which banks as well as turns the airplane.

ing pedals connected by control members to the rudder surfaces for operating the rudder surfaces in unison in the same direction to provide tuming movements of the airplane, a control stick mounted to swing about a pivot in a plane at a right angle to the longitudinal axis of the fuselage,-said control stick-being interconnected respectively to said control -members at points spaced on opposite sides of said pivot, the movement of said control stick being effective to vary the response of one rudder surface relative to the other from unequal movements in the same directiOnto movements in opposite directions to pro- 

